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2005-8 Previous Version

Policy statement

It is proposed to make the following changes to the existing ARIN IPv6
policy:

Define an additional end site assignment size of /56. This /56 assignment should be considered the general case, intended for small office, household, and personal networks, and other small and medium-sized deployments where the number of potential subnets exceeds 1, but is not expected to exceed 256.

Amend the existing policy regarding /48 end-site assignments to refer specifically to assignments to large enterprise and corporate end-site environments where there is a requirement for more than 255 subnets at the end site.

Amend the evaluation threshold calculation to be based on a default end site assignment size of a /56. Further end-site assignment information should be provided to ARIN in order to use a different average end-site assignment size for HD-ratio calculation purposes.

Policy Rationale

The key benefit of IPv6 is its large address space, and a fundamental assumption motivating its adoption is that with IPv6, sufficient address space will always be available to ensure that users can obtain sufficent public address space for their needs. Projections for IPv6 address consumption over the next 50-100 years indicate that there are scenarios (depending on one's assumptions) in which a signficant percentage of the total IPv6 address space could be handed out, raising the possibility that address allocation policies will then need to be revised to become significantly more conservative to ensure that the IPv6 address space does not become exhausted. Given the IPv4 experience, in which early adopters were able to acquire large amounts of address space easily, but later adopters were not, and the resultant problems this has caused, it would be preferable to take steps now to signficantly reduce the likelyhood of ever needing to make such a change, especially if changes can be made with minimal impact.

The RIR communities adopted address allocation policies in 2002 in which the default assignment to end sites was assumed to be a /48 in many cases. For SOHO users (e.g., home users and small businesses), being given enough address space to number 65,536 subnets seems excessive given their anticipated needs. Changing the default assignment size to a
/56 allows for numbering 256 subnets, still a large number. Making such a change would save roughly two orders of magnitude of address space.
That is, for any projection made assuming a /48 assignment, assigning /56s instead would result in roughly 100 times less total consumption.

The goal of this policy proposal is not to make it impossible for end sites to obtain a /48. Rather, it is intended to make the default assignment size a /56 in the vast number of cases where a /48 seems profligate. In those cases where the end site can argue that it has a need for more than 256 subnets, a /48 should be given out.

Background information:

"Issues Related to the Management of IPv6 Address Space", by Thomas Narten.
http://www.ietf.org/internet-drafts/draft-narten-iana-rir-ipv6-considerations-00.txt

Similar policy proposal submitted to APNIC (includes detailed background and pointers to more background information than is included here).
http://www.apnic.net/docs/policy/discussions/prop-031-v001.txt

State of related discussion in other RIRs: See section "Situation in other RIRs" in http://www.apnic.net/docs/policy/discussions/prop-031-v001.txt

IETF revisitation of RFC 3177 "IAB/IESG Recommendations on IPv6 Address Allocations to Sites", the document in which the case for assigning /48s was made.
http://www.ietf.org/internet-drafts/draft-narten-ipv6-3177bis-48boundary-00.txt
(note: this document was adopted as a WG item by the IPv6 WG at IETF
63 in August.)